OBJECTIVE:
To estimate the prevalence of wheezing in the chest among adults, and to explore
the effect of some variables on the prevalence of this condition.METHODS: This was a prospective cohort study on individuals born in the
city of Pelotas (Southern Brazil) in 1982. A total of 4,297 subjects was traced
in 2004-5, representing 77.4% of the original cohort. Data were collected by
means of interviews using the ISAAC (International Study of Asthma and Allergies
in Childhood Steering Committee) questionnaire. Associations between the outcome
"occurrence of wheezing in the chest within the 12 months prior to the interview"
and the variables of socioeconomic, demographic and birth characteristics were
tested by means of multivariable analyses, using Poisson regression.RESULTS: The prevalence of wheezing over the preceding year was 24.9%.
Among the individuals reporting wheezing, 54.6% reported difficulty in sleeping,
and 12.9% reported difficulty in speaking due to wheezing. The prevalence of
wheezing in the chest was significantly higher among women. This association
was maintained in analyses adjusted for non-white skin color, family history
of asthma and low socioeconomic level. Among men, there was no significant association
in the analyses adjusted for skin color and family income at birth. Family histories
of asthma and poverty throughout life presented significant associations with
wheezing in the chest. For both sexes, there were no associations with the variables
of birth weight and breastfeeding duration.CONCLUSIONS: The prevalence of wheezing in the chest was high, and subjects
with low family income at birth were more likely to have had wheezing in the
chest over the preceding year.

The prevalence,
incidence and severity of asthma are increasing worldwide. Although the number
of studies on asthma in childhood is increasing,18 most of the data
on the prevalence of asthma among young adults comes from developed countries.5
Studies in middle or low-income countries are needed for better understanding
of the epidemiology of this disease among adults.

The various diagnostic
methods used in clinical practice are still little used for epidemiological
surveys, particularly for household-based surveys. In most such studies, the
diagnosis is based on reported symptoms, especially wheezing in the chest.18
Population-based studies may also help in understanding the role of socioeconomic
factors and early influences on the epidemiology of asthma.

The aims of the
present study were to estimate the prevalence of wheezing in the chest among
young adults and to explore the effect of some independent variables on occurrences
of this morbidity.

METHODS

All the births
that occurred in hospitals in the city of Pelotas in 1982 were identified. The
mothers were interviewed and the newborns were weighed. This population was
followed up on different occasions. In 2004-5, all the members of the cohort
were sought, and a monitoring rate of 77.4% (N = 4,297) was achieved. Details
of the methodology of the cohort have already been published.4,15,16

To define the outcome
of the present study, the questionnaire of the International Study of Asthma
and Allergies in Childhood Steering Committee (ISAAC) was used.3,18
This has already been validated in Brazil.1 Firstly, the subjects
were asked whether they had ever had wheezing in the chest during their lives.
Then, those who answered affirmatively were asked how many crises of wheezing
in the chest they had had over the past year and whether they had any family
history of paternal or maternal asthma.

The independent
variables gathered were: sex; self-reported skin color (White or Black/Mixed);
family income reported by the mother in 1982, in minimum monthly wages (MMW);
family income in 2004-5 (in MMW); birth weight, in grams; and duration of breastfeeding,
in months. Based on the income at birth and present income, the change in income
between 1982 and 2004-5 was defined and categorized into four groups: always
poor; non-poor to poor; poor to non-poor; and never poor. The individuals within
the lowest tercile of income were defined as poor.

Bivariate analyses
were based on the chi-square test for heterogeneity or linear trend. Poisson's
regression was used for multivariable analysis stratified by sex and in accordance
with a conceptual model in which the variables of skin color, family history
of asthma, maternal schooling level and family income at birth were grouped
into the first level. The variables of birth weight and duration of breastfeeding
were analyzed separately, in the second and third levels, respectively. For
the adjusted analysis, all the variables with p < 0.20 were kept in the model.

Verbal informed
consent was obtained from the adults responsible for the children during the
phase of the study from 1982 to 1986, as was the common practice at that time,
when there was no ethics committee at the Federal University of Pelotas. For
the more recent phases, the university's ethics committee, which is affiliated
to the National Council for Research Ethics (Conselho Nacional de Ética
em Pesquisa, CONEP), approved the study and written informed consent was
obtained from the participants.

RESULTS

Among the young
adults who answered the questionnaire on asthma, 2,231 (52.0%) reported that
they had had wheezing in the chest at some time during their lives. A total
of 1,067 members of the cohort (24.9%) reported wheezing in the chest over the
past year. The mean number of crises of wheezing reported by these individuals
over the 12 months preceding the interview was 5.7, with a median of two crises.
Among those who reported wheezing in the chest over the past year, 54.6% said
they had difficulty in sleeping and 12.9% had difficulty in speaking, consequent
to the crises. The prevalence of dry coughing at night without colds, over the
12 months preceding the interview, was 38.7%, while 14.4% of the interviewees
reported wheezing in the chest after doing physical exercise. Family histories
of asthma (father or mother) were reported by 8.8% of the interviewees.

Table
1 presents the prevalence of wheezing in the chest over the 12 months preceding
the interview, according to the independent variables and stratified by sex.
For both sexes, the prevalence was greater among individuals with a family history
of asthma. Among the women, mixed or Black skin color and low socioeconomic
level were associated with greater prevalence of wheezing. Among the men, those
who had never been poor presented lower frequency of this outcome. For both
sexes, birth weight and duration of breastfeeding did not present associations
with occurrences of wheezing in the chest.

Table
2 shows the prevalence ratios in the crude and adjusted analyses for the
men. Individuals with a family history of asthma presented a risk of wheezing
in the chest that was around twice the risk among those without a family history
of this condition. Individuals who had never been poor presented lower risk.
Even after adjusting for possible confounding factors, skin color, birth weight
and duration of breastfeeding were not associated with a risk of wheezing in
the chest.

Table
3 presents the results for the women. Skin color and family history of asthma
continued to be associated with wheezing after adjustments. Low family income
at birth and poverty throughout life were associated with this outcome, and
also in the adjusted analysis. The absence of effects from the variables of
birth weight and duration of breastfeeding on the prevalence of wheezing in
the chest among the women persisted in the adjusted analysis.

DISCUSSION

Around a quarter
of the young adults in the 1982 Pelotas cohort reported wheezing in the chest
over the past year. In the National Health and Nutrition Examination Survey
(NHANES III), conducted in the United States, the prevalence of wheezing in
the chest over the 12 months preceding the interview, among adults aged 20 years
and over was 16.4%, while the prevalence of a medical diagnosis of asthma was
4.5%.2 In the Behavioral Risk Factor Surveillance System of 2000
(BRFSS-2000), 7.2% of the adults living in the United States reported that a
doctor had told them that they had asthma and that the symptoms continued until
the time of the interview.8 In Australia, the prevalence of wheezing
in the chest over the last year ranged from 17% to 29% among adults (20 to 44
years of age).17 In a European study covering several countries,
the prevalence of asthma among young adults (20 to 44 years of age) was 4.5%,
although there was great variability between the countries.9 The
study by Pearce et al13 showed that there was high concordance between
the instruments used in ISAAC and the European Committee of Respiratory Health
Survey,13 which allows comparison between our findings and those
from the European study.

In the present
study, the women presented a risk of reporting wheezing in the chest that was
12% greater than the risk among the men. This corroborates the data from BRFSS-2000,
NHANES III for wheezing in the chest2 and another Brazilian study
on asthma symptoms.11 However, it needs to be borne in mind that,
in childhood, the prevalence of wheezing in the chest is greater among boys
than among girls.6 In our study, the Black or Mixed women presented
a greater risk of wheezing in the chest, thus confirming the data of BRFSS-2000,
in which Blacks presented greater occurrence of asthma than did Whites.8
On the other hand, in NHANES III, the prevalence of wheezing in the chest over
the past year was slightly higher among Whites than among Blacks.2
Thus, there is no agreement between the studies regarding this association.

Our results showed
that individuals with lower income presented a higher risk of wheezing in the
chest, which was also in agreement with data from BRFSS-2000.8 A
study conducted in Pelotas on adults aged 20 to 69 years showed that those with
lower family income presented a higher risk of asthma symptoms than did those
with higher family income, both in the crude analysis and in the adjusted analysis.11
In another cohort study carried out in Pelotas, the prevalence of wheezing in
the chest was greater among the young people of low socioeconomic level, both
during childhood and at the start of adolescence.6,12 In a previous
follow-up on this cohort10 that was conducted at the time of the
military call-up for the young men, the frequency of wheezing in the chest was
greater among those of high family income. These data are concordant with the
"hypothesis of hygiene", which proposes that infections during childhood may
provide protection against asthma during adulthood. In the present analysis,
which was conducted among individuals of both sexes five years after the latter,
the association between family income and wheezing in the chest was in the opposite
direction. In the earlier paper, a hypothesis of information bias was raised,
given that reports on asthma could be different between young people of high
and low socioeconomic level.10 By cross-referencing the reports from
the two interviews, among individuals who said at the military interview that
they had had wheezing in the chest during the past year, the following percentages
reported wheezing in 2004-5: 55.4% of the lowest tercile of income, 45.4% of
the middle tercile and 42.7% of the highest tercile. This suggests that some
young men with high income erroneously said that they had wheezing at the time
of the military call-up, possibly to avoid recruitment. This bias may explain
the discrepancy between the results.

The effect of changes
of income on the frequency of wheezing in the chest showed that individuals
exposed to poverty, whether during childhood or during adulthood, presented
greater risk. It was not possible to detect whether exposure to poverty during
childhood was more harmful than exposure during adulthood, or vice versa.

The study among
the recruits also showed that prolonged breastfeeding increased the risk of
wheezing in the chest,10 which was not confirmed in the present analysis.
On the other hand, recent meta-analyses have shown that breastfeeding has a
protective effect or no effect on occurrences of asthma.7,14

It was decided
to present the analysis with stratification by sex, given that a recent paper
showed that the risk factors for wheezing in the chest among adolescents aged
10 to 12 years were very different between boys and girls.12 However,
among young adults, little difference in the risk factors for wheezing was detected
between men and women.

Some limitations
of the present study must be taken into consideration. The diagnosis of asthma
was based on symptoms of wheezing in the chest, which although being a good
indicator for occurrences of asthma, do not constitute a confirmed diagnosis.
However, there is no gold-standard method for diagnosing this disease. The symptom
of wheezing in the chest is used internationally and has been shown to be the
best option for epidemiological studies. Furthermore, although a recall period
of 12 months was used, as recommended in the literature, there is the possibility
of some degree of memory bias.

This article is
based on data from the study "Pelotas birth cohort, 1982" conducted by Postgraduate
Program in Epidemiology at Universidade Federal de Pelotas.
The 1982 birth cohort study is currently supported by the Wellcome Trust initiative
entitled Major Awards for Latin America on Health Consequences of Population
Change. Previous phases of the study were supported by the International Development
Research Center, The World Health Organization, Overseas Development Administration,
European Union, National Support Program for Centers of Excellence (PRONEX),
the Brazilian National Research Council (CNPq) and Brazilian Ministry of Health.
This article underwent the same peer review process as for other manuscripts
submitted to this journal. Both authors and reviewers are guaranteed anonymity.
Editors and reviewers declare that there are no conflicts of interest that could
affect their judgment with respect to this article.
The authors declare that there are no conflicts of interest.